Cons have a tons of stuff to do: gaming--board games, rope playing games, video games, card games--at all hours of the day and night; panels on everything from writing to movies to science; cosplay; film festivals, filking; dances, etc. You can buy incredible fantasy and science fiction themed art for reasonable prices and a wide variety of other cool merchandise.
If you have children, most cons have a children's track with activities specifically designed for the younger ones. You can often meet famous and not-so-famous authors and artists, at bigger ones actors, as well.
I will be in the merchant's room for some of the time, trying to sell my novels. Wish me luck on that, and I'll have a full report in this spot next week.
You can find out more about Archon on their website.
If you've been to a con, leave a comment about your experience.